NAME

SYNOPSIS

DESCRIPTION

As mentioned in Encode, encodings are (in the current
implementation at least) defined as objects. The mapping of encoding
name to object is via the %Encode::Encoding
hash. Though you can
directly manipulate this hash, it is strongly encouraged to use this
base class module and add encode() and decode() methods.

Methods you should implement

You are strongly encouraged to implement methods below, at least
either encode() or decode().

->encode($string [,$check])

MUST return the octet sequence representing $string.

If $check is true, it SHOULD modify $string in place to remove
the converted part (i.e. the whole string unless there is an error).
If perlio_ok() is true, SHOULD becomes MUST.

If an error occurs, it SHOULD return the octet sequence for the
fragment of string that has been converted and modify $string in-place
to remove the converted part leaving it starting with the problem
fragment. If perlio_ok() is true, SHOULD becomes MUST.

If $check is false then encode
MUST make a "best effort" to
convert the string - for example, by using a replacement character.

->decode($octets [,$check])

MUST return the string that $octets represents.

If $check is true, it SHOULD modify $octets in place to remove
the converted part (i.e. the whole sequence unless there is an
error). If perlio_ok() is true, SHOULD becomes MUST.

If an error occurs, it SHOULD return the fragment of string that has
been converted and modify $octets in-place to remove the converted
part leaving it starting with the problem fragment. If perlio_ok() is
true, SHOULD becomes MUST.

If $check is false then decode
should make a "best effort" to
convert the string - for example by using Unicode's "\x{FFFD}" as a
replacement character.

If you want your encoding to work with encoding pragma, you should
also implement the method below.

->cat_decode($destination, $octets, $offset, $terminator [,$check])

MUST decode $octets with $offset and concatenate it to $destination.
Decoding will terminate when $terminator (a string) appears in output.
$offset will be modified to the last $octets position at end of decode.
Returns true if $terminator appears output, else returns false.

If your encoding can work with PerlIO but needs line buffering, you
MUST define this method so it returns true. 7bit ISO-2022 encodings
are one example that needs this. When this method is missing, false
is assumed.

Why the heck Encode API is different?

It should be noted that the $check behaviour is different from the
outer public API. The logic is that the "unchecked" case is useful
when the encoding is part of a stream which may be reporting errors
(e.g. STDERR). In such cases, it is desirable to get everything
through somehow without causing additional errors which obscure the
original one. Also, the encoding is best placed to know what the
correct replacement character is, so if that is the desired behaviour
then letting low level code do it is the most efficient.

By contrast, if $check is true, the scheme above allows the
encoding to do as much as it can and tell the layer above how much
that was. What is lacking at present is a mechanism to report what
went wrong. The most likely interface will be an additional method
call to the object, or perhaps (to avoid forcing per-stream objects
on otherwise stateless encodings) an additional parameter.

It is also highly desirable that encoding classes inherit from
Encode::Encoding
as a base class. This allows that class to define
additional behaviour for all encoding objects.

to create an object with bless{Name=> ...},$class
, and call
define_encoding. They inherit their name
method from
Encode::Encoding
.

Compiled Encodings

For the sake of speed and efficiency, most of the encodings are now
supported via a compiled form: XS modules generated from UCM
files. Encode provides the enc2xs tool to achieve that. Please see
enc2xs for more details.